Cyclohexane recovery



lJune 16, 1959 vc. M. KRoN cYcLoHExANE RECOVERY Filed Aug. 16, 1957United States Patent Gfiee CYCLOHEXANE RECOVERY Carl M. Kron, Phillips,Tex., assignor to Phillips Petroleum Company, a corporation of DelawareApplication August 16, 1957, Serial No. 678,713

7 Claims. (Cl. 2150-666) This invention relates to the recovery ofcyclohexane from a hydrocarbon mixture. In one aspect it relates to therecovery of cyclohexane from natural gasoline or straight run gasoline.In another aspect it relates to the recovery of cyclohexane from narrowboiling range fraction of mixed cyclic hydrocarbons containing carbon`tetrachloride and sulfur compounds.

Cycloparains, such as cyclohexane, ud wide use as solvents and asstarting or intermediate materials in chemical reactions. Usually it isdesirable that the cycloparalns be available in a relatively pure state.For example, when cyclohexane is used as a solvent or diluent n thepolymerization of olens to solid polymers it is desirable that thismaterial be free from sulfur compounds and other materials which aredetrimental to the polymerization catalysts. One of the sources ofcyclohexane is natural gasoline which frequently must be transportedover long distances by pipeline. As an aid in the transportation ofnatural gasoline and to eliminate the problem of wax deposition, carbontetrachloride is frequently added to this material. Another source ofcyclohexane is straight run gasoline from crude oils. This material alsofrequently contains carbon tetrachloride as a result of treatment ofequipment, eg. well casings, pipelines, in the oil elds with chlorinatedsolvents. This invention is concerned not only with the removal ofsulfur and other materials which are detrimental to the polymerizationcatalysts but also with the separation of cyclohexane from carbontetrachloride, which can also act as a catalyst poison.

It is an object of this invention to provide improved process for therecovery of cyclohexane.

It is another object of this invention to provide an improved processfor recovery of cyclohexane from narrow boiling range gasolinescontaining carbon tetrachloride.

Yet another object `of this invention is to recover cyclohexane from anarrow boiling range fraction of mixed cyclics containing sulfurcompounds and carbon tetrachloride.

These and other objects of the invention will become more readilyapparent from the following detailed description and discussion.

The foregoing objects are realized by processing a narrow boiling rangefraction of mixed cyclics from a natural gasoline containing carbontetrachloride in a first fractionation zone wherein materials lighterthan cyclohexane are removed, treating the fractionation bottoms toremove sulfur compounds and further processing the bottoms in a secondfractionation zone to remo-ve materials heavier than cyclohexane andrecover a cyclohexane product free from carbon tetrachloride and sulfurcompounds.

,l In one aspect of the invention the irst fractionation zone isoperated to provide an overhead product containing at least about12`volume percent of material boiling above'methylcyclopentane includingat least about 4.5 volume percent cyclohexane, the acid treating iscarried 2,891,100 Patented June 16, 1959 out utilizing an acid having aWeight percent concentration of at least about 7() percent and thesecond fractionation zone is operated to provide an overhead productcontaining notmore than about 1li volume percent of material boilingbelow cyclohexane and not more than about 6 volume percent of materialboiling above cyclohexane.

Cyclohexane purified by the aforedescribed process can be used for avariety of purposes. One application is the useof this material as adiluent and solvent in the polymerization of olens to solid polymers inthe presence of chromium oxide catalyst, containing hexavalent chromium,associated with' an additional or supporting material. The followingdiscussion will be directed to this specific application however, thisis not intended in any way to limit the scope of the invention, which isdirected broadly to the purification and recovery of cyclohexane i forany suitable purpose.

Various olens can be converted to solid polymers including, for example,monoolens like ethylene, propylene, butylenes, etc. Also variousmonoolens can be polymerized with each other or with diolefns such asbutadiene and isoprene, etc.

Solid olelin polymers are prepared usually by contacting the olen to bepolymerized with a catalyst at an elevated temperature and pressure,preferably in the presence of the solvent or diluent material. Thetemperature required for polymerization varies over a Wide range;however, usually it is preferred to carry out the reaction at atemperature between about 150 F. and about 450 F. The particulartemperature to be ernployed in each individual case depends on thecatalyst used, the oleiins to be polymerized and the operatingconditions employed such as pressure,I space Velocity, diluent olefinratio, etc.

The polymerization pressure is often maintained at a. suicient level toassure a liquid phase reaction, that is at least about to 300 p.s.i.g.,depending upon the type of feed material and the polymerizationtemperature. Higher pressure up to 500 to 700 p.s.i.g. or higher can beused, if desired. When utilizing a fixed catalyst bed the space velocityvaries from as low as 0.1 to about 20 Volumes of feed per volume ofcatalyst per hour, with the preferred range being between about 1 andabout 6l In this type of operation the catalyst concentration inV thereaction zone is usually maintained between about 0.01 and about l0percent by weight and the feed residence time can be from 10 minutes orless to 10 hours or more.

A preferred polymerization method is described in detail in a copendingapplication of Hogan and Banks, Serial No. 573,877, filed March 26,1956, now U.S. Patent 2,825,721. mium oxide catalyst containinghexavalent chromium, with silica, alumina, silica-alumina, zirconia,thoria, etc. In one embodiment of this application, olens arepolymerized in the presence of a hydrocarbon diluent, for example, anacyclic, alicyclic or aromatic compound which is inert and in which theformed polymer is soluble. The reaction is ordinarily carried out at atemperature between about F. and about 450 F. and usually under apressure suflcient to maintain the reactant and diluent in the liquidstate. The polymers produced by this method, particularly the polymersof ethylene, are characterized by having an unsaturation which isprincipally either transinternal or terminal vinyl, depending on theparticular process conditions employed. When low reaction temperatures,about 150 F. to about 320 F., and a mobile catalyst are used forpolymerization,'the product polymer is predominantly terminal vinyl Thisparticular method utilizes a chro-` in` structure. When polymerizationis carried out at higher temperatures and in a xed catalyst bed, thepolynier has predominantly transinternal unsaturation. Polymers preparedby both methods are also characterized by their. high. densities andhigh percentage of crystallinity atnormal atmospheric temperatures.

The solvent or diluent employed in the polymerization reaction` includesin general, paraflins which dissolve the polymers at the temperatureemployed inthe reaction zone. Among the more useful solvents areparainshaving between about 3 and 12 carbon atoms per molecule, such as, forexample, propane, isobutane, n-pentane, isopentane, isooctane, etc., andpreferably those paraii'ins having 5 to l2 carbon atoms per molecule.Also useful in the polymerization reaction are alicyclic hydrocarbons,such as cyclohexane, methylcyclohexane, etc; Aromatic diluents are alsoused, however, in some instances they (or impurities therein) tend toshorten the catalyst life, therefore their use will depend on theirnportance of catalyst life. All of the foregoing and in addition,other hydrocarbon diluents which are relatively inert and in 'the liquidstate at the reaction conditions may also be employed in carrying outthe reaction of olefms to form solid polymers.

In carrying out the invention in one embodiment thereof a naturalgasoline fraction containing mixed cyclic hydrocarbons contaminated withcarbon tetrachloride and` sulfur compounds is introduced to afractionation zone wherein a major portion of the cyclohexane isseparated as .bottoms product and carbon tetrachloride passes overheadvwith lower boiling materials. The components which are presentin thefeed to the fractionation tower can comprise a relatively wide boilingrange of materials, however, usually it is desirable that the materialtreated have a narrow boiling range, containing, for example, materialsboiling between about 150 F. and about200 F. A typical fraction havingsuch a boiling range contains, compounds such as Z-methylhexane and2,3-dimethylpentane, 1,1-dimethylcyclopentane, 3,3-dimethylprentane,etc. which are higher boiling than cyclohexane and2,2,3-trimethylbutane, 2,4-dimethylpentane, 2,2-dimethylpentane,methylcyclopentane, benezene, S-methylpentane, normal hexane, etc. whichare lower boiling than cyclohexane. In addition, the fraction as stated,contains carbon tetrachloride and various types of sulfur compounds.Because of the closeness of the boiling range of thevarious compoundsithas been found that in order to remove all of the carbon tetrachlorideit is necessary in thefractionation zone to take overhead a productcontaining at least about 12 percent by volume of materials boiling"above methylcyclopentane and including at least about 4.5 percentbyvolume of cyclohexane. To obtain this result a fractionation towercontaining a large numberof trays is necessary, namely about at least 50trays and preferably at least about 100 trays. The fractionation Vcan becarriedk out over a relatively wide range of pressure, for example, fromto 100 p.s.i.g. or higher. Corresponding temperatures to give a desiredseparation are in the range of between about 150 F. and about 290 F. Theoverhead from the fractionation zone can be further processed to recovermethylcyclopentane and other components if desired. These materials ndvalue in various uses, for example, methylcyclopentane can be utilizedas a solvent or this material can be isomerized to cyclohexane.

' The bottoms from the fractionation zone, which are substantially freefrom carbon tetrachloride, are passed through a treating step forremoval of sulfur compounds. Various treating agents can be utilized forthis purpose including sulfuric acid, hydrolluoric acid, aluminumchloride, clays, bauxite, etc. Because of the effect of sulfur and about20 parts per million. When using sulfuriciacid' as the treating agent,it has been found that in order to provide this reduction in sulfurcontent it isnecessary` to..

maintain the sulfuric acid strength in the treating zone over 70 percentby weight and preferably over 75 percent by weight. The treating processis usually carried out at normal atmospheric temperatures and pressuresusing one part of acid for 75 to 250` parts by weight of hydrocarbons.

Following desulfurization, the fractionation-bottoms are passed througha conventional treatment for the removal of acid, such as for examplethrou-gh a caustic treater,

after which this material is introduced to a second fractionation zone.In the latter zone, materials heavier than cyclohexane are removed as abottoms stream and the desired cyclohexane product. is takenoverhead. Toassure the desired purity of the overhead product it is necessary thatthis material contain not more than about l1 percent by volume ofmaterials boiling belowv cyclohexane and not more than about 6 percentby volume of-higher boiling components.

In order to more clearly describe the invention-and provide a betterunderstanding thereof, reference isV had to-the accompanying drawingwhich is a diagrammatic illustration of fractionating` vessels andtreating systems suitable for carrying out-the invention. Referringtothe drawing, a narrow boiling fraction of mixed-cyclic compoundsboiling between F. and 200 F. is introduced toa demethylcyclopentanizer4 wherein separation is effected between cyclohexane and the lightermaterials in the feed. The overhead vapors from this tower, com'-prisingmethylcyclopentane and various dimethylpentanes with somecyclohexane, pass through conduit 6 andA soidum sulfide treater Swherein hydrogen sulfide is removed, and then are introduced throughUconduit 10 to fractionator 12. The overhead from the fractionator,comprising essentially methylcyclopentane and lighter components, passesthrough conduit 14, condenser 16' and; The material in the accumulatoris into accumulator 18. withdrawn through pump 20with a portionbeingreturned, to the fractionator as reliux through conduit 22.'

and the remainder being yielded through conduit 24. The variousdimethylpentanes and cyclohexane which make up the bottoms product fromthe fractionator are yielded through conduit 26 and cooler 28.

. The. bottoms from the. demethylcyclopentanizer 4,

which are concentrated in cyclohexane, are substantially free fromcarbon tetrachloride, however, this stream still'v contains varioussulfur containing compounds. To effect the removal of these compoundsthe bottoms product is withdrawn from the demethylcyclopentanizerthrough conduit 30, admixed with sulfuric acid from conduit40: andintroduced to treating vessel 32. The acid reacts to.

remove sulfur compounds and the hydrocarbon and acid are resolved intoseparate phases within this vessel. A weir is provided .in the treatingVessel and the hydrocarbon phase overflows this weir and is withdrawnthrough` through conduit 54 and entering a second fractionator 56,which'is designated as a deoiler. Caustic is removed 1.

fromvessel 44'through pump 48 and recycled through conduit 52. Conduits46 and 50 are provided for the removal of spent caustic and the additionof freshcaustic,

respectively.

Within the deoiler 56 the desulfurized hydrocarbonl stream is subjectedto a further separation whereby heavy oils are removed from thecyclohexane. i `These oils pass from the deoiler bottom through conduit70 and cooler 72. The overhead from the deoiler, comprising prineTablell` cipally cyclohexane, with a small quantity of lower andFrootionatorw OHP Polymor- Deouor (56) 0111 higher boiling materials isremoved through conduit 58 5 ization and condenser 60 and passes toaccumulator 62. The ac- Run No. cumulated material is withdrawn throughpump 64` with :'illg 5gg magg lllftl; Bijfg b c n u n l a portion beingreturned to the deoiler through condu1t urities, Content, iii/hr. p.p.m.impurities, 66 as reflux and the remainder being passed from the unit Lpercent LV percent LV percent through conduit 68. As desired thecycloheXane product 1 10 7 3 3 can be utilized as a solvent, as anintermediate in various 2: 10:1. 2j? 11g l? gig chemical reactions orfor any other appropriate use.

gig 4g E g Preferably the material obtained in this specic `opera- 5:1516 716 13S s 101.7 tion is utilized as a solvent and diluent inpolymerization 6- 11-2 32. 134 12 lll-9 f l h f h 7 11.2 3.2 150 7 11.4o o e ns in t e presence o a c romium oxide catalyst, gg gg gg g 10,59.2 containing heiravalent chromium, associated with a sup 10 16.6 8.7243 12 11.0 porting material. ii 12.1 5.0 230 7 10.2

The preceding discussion has been directed to a preg ggg .l'g ferredembodiment of the invention, however this is not 14,- 13s 49 278 11 10:3intended in any limiting sense but is merely illustrative of theinvention, which broadly comprises recovering T urbdimemc analysis. andpurifying cyclohexane from a hydrocarbon mixture. clshtrsthnpwohexnw d fd d l 1 The following data is presented in illustration of a to aulofesieinreeno correspon mg emersamp es commercial application of theinvention. Heavlef than methylcylopntanei e Ethylene polymerized .in thepreseuce'of a catalyst comprising 2.5 EXAMPLE percent by weight ofchromium as chromiiirn'omde, 'containing 2.2 percent by weitghthextaveiit titlironiliurn, ilca-tlluminla. prepafreg by impregna ing paric a es ica-a umiua 0 wi aso utiono c roinium The followmg tets weremade 1n a commefclal un oxide followed by drying and activation in airat gradually increasing similar to the unit illustrated in theaforedescribed temperatures upto 95 F., under tno following conditions:drawing. In each operation the feed material comprised Ethylene feed me160,000 1b. /hn a narrow boiling range fraction from a natural gasolinegyleiohexanefeeg ngt gagpntoiu/hnt i o O ymel CODCBD 191 10U. W eI'CeIlcontammgrmatenflls betwen about 150 F' and about Catalyst concentrationinreaetor 0.5 wtgercent. 200 F. I'he acid used in each case was 93%fresh 'iressuro 420 psig. acid. The results of a series of operationscarried out empemme" 290 F' on different days are set forth in Tables Ithrough III.

Table 1 Fractionator (4) Deoller (56) Volumes, g.p.d. v

A B C A B C Food 107,000 107,000 97, 000 70,000 72,000 65,000 Reflux435,000 435,000 435,000 140,000 144,000 144,000 Bottoms Product.. 73,00072,000 5,000 4,000 53,000 3,000 overhead Product. 34,000 35, 000 32,00006, 000 07, 000 02, 000 Temperatures, i F.:

Bottom 279 279 280 275 273 272 Feed 257 25s 25s 250 250 249 Accumulator-151 150 153 118 119 124 Top 233 238 239 251 250 250 Pressure, p. i

40 4o 40 i9 19 19 13 13 13 i0 i0 i0 47 47 47 25 25 25 Table I abovepresents representative feed rates a-nd Table III operating conditionsfor three dilerent commercial runs. In TableII are presented pertinentdata relating to the Acid Con. Sulfur con. composition of thefractionator overhead product and de- Run ceirirtration Ftenttoi nReaction oiler overhead product and data on. the polymeriaation gclrltalg? ff' ih /hj reaction rate obtained when polymerizing ethylene in theHiSOt OHP ILD-D1- presence of the deoiler overhead product and chromiumoXide catalyst, containing hexavalent chromium, asso- Si 24g ciated witha supporting material. Referring to Table 79 7 232 Il it is to be notedthat when the overhead product from 9284 121s the fractionator containsless than about l2 percent of materials boiling abovemethylcyclopentane, or when the cyclohexane content of the fractionatoroverhead product is less than about 4.5 percent, or when the deoileroverhead product contains more than about ll volume percent of materialsboiling below cyclohexane that the polymerization reaction rate is lowerthan 150` lbs/hr.

Table III presents a relationship between polymerization reaction rateand acid concentration in the treater. It is to be noted that thereaction rate with an acid concentration of 69 weight percent is 0. Itis also to be noted that high reaction rates are obtained in the rangeof 74 to 93 percent acid by weight.

n Turbidimetric analysis.

hydrocarbons containing cyclohexane and said impurities, introducingsaid fraction -to la Airst fractionation zone, taking overhead from saidzone a fraction containing at least .about 1-2 'volume percent ofmaterial boiling above methylcyclopentane 'including at least about 4.5volume percent -cyclohexane and carbon tetrachloride, treating thebottoms from the fractionation zone with sulfuric acid, yintroducing thetreated material to a second fractionation zone wherein heaviercomponents are separated Vfrom ythe Ycyclohexane 4and recovering fromsaid second zone an overhead product containing not more than l11 volumepercent 'of materials boiling below cyclohexane and not more than about6 volume percent of lmaterials boiling above cyclohexane.

2. The process of'claim 1 in`which the bottomsfrom i the firstfractionatiorrzone are treated Iwith sulfuric acid having aconcentration of atleast 70 percent.

3. A process for recovering cyclohexane from a narrow boiling rangefraction of mixed cyclic 'hydrocarbons containing carbon tetrachlorideand sulfur compounds as impurities which comprises 'introducing saidfraction to a first fractionation zone, taking -overhead from said zonea-fraction=containing'atleast about 12 volume percent of materialboili-ng above methylcyclopentane including at least about 4.5 volumepercent cyclohexane and carbon tetrachloride, treating the bottoms fromthe fractionation zone with sulfuric acid, introducing the treatedmaterial to a second fractionation zone wherein heavier components areseparated from the cyclohexane and recovering from said second zone anoverhead product containing not more than v1l volume percent ofmaterials boiling Vbelow cyclohexane and not more than about 6volumepercent of materials boiling above cyclohexane.

4. A process for recovering cycloheXane from a hydrocarbon fractioncontaining carbon tetrachloride and sulfur compounds as impurities whichcomprises separating from said hydrocarbon fraction a narrow boilingfraction of mixed cyclic hydrocarbons containing cyclohexane and saidimpurities, introducing said fraction to a first fractionation zone,taking overhead from said zone carbon tetrachloride, a portion of thecyclohexane and components boiling lower than cyclohexane, said overheadcontaining at leastabout 12 volume percent ofcompounds boiling abovemethylcyclopentane, including at least about 4.5 volume percentcyclohexane, treating the bottoms from the fractionation zone with atreating agent to remove sullfur compounds, introducing the treatedmaterial to a second fractionation zone wherein components boilinghigher than cyclohexane are separated from the cyclohexane `andrecovering from said second zone an overhead product concentrated incyclohexane.

5. The process of claim 4 in 'which the bottoms from the rstfractionation zone are treatedwith sulfuric acid having a concentrationof at least 70 percent.

6. A- process for recovering cyclohexane from a hydrocarbon fractioncontaining carbon tetrachloride and sulfur compounds-as impurities whichcomprises separating 'from said hydrocarbon fraction a narrow boilingfraction of mixed cyclic hydrocarbons containing cyclohexane and saidimpurities, introducing said fraction to a rst fractionation zone,taking overhead from said zone carbon tetrachloride, a portion of thecyclohexane and components boiling lower than cyclohexane, treating thebottoms from the vfractionation zone with a treating agent to removesulfur compounds, introducing the treated material to a secondvfractionation zone wherein components boiling higher than cyclohexaneare separated from the cyclohexane, and recovering from said second zonean overhead product concentrated in cyclohexane, containing not morethan about l1 volume percent of lower boiling materials and not morethan about 6 volume n percent of materials boiling above cyclohexane.

`7. The process of claim 6 in which the bottoms from the rstfractionation zone are treated with sulfuric acid having a concentrationof at least 70 percent.

References Cited in the le of this patent UNITED STATES PATENTS

1. A PROCESS FOR RECOVERING CYCLOHEXANE FROM GASOLINE CONTAINING CARBONTETRACHLORIDE AND SULFUR COMPOUNDS AS IMPURITIES WHICH COMPRISESSEPARATING FROM SAID GASOLINE A NARROW BOILING RANGE FRACTION OF MIXEDCYCLIC HYDROCARBONS CONTAINING CYCLOHEXANE AND SAID IMPURITIES,INTRODUCING SAID FRACTION TO A FIRST FRACTIONATION ZONE, TAKING OVERHEADFROM SAID ZONE A FRACTION CONTAINING AT LEAST ABOUT 12 VOLUME PERCENT OFMATERIAL BOILING ABOVE METHYLCYCLOPENTANE INCLUDING AT LEAST ABOUT 4.5VOLUME PERCENT CYCLOHEXANDE AND CARBON TETRACHLORIDE, TREATING THEBOTTOMS FROM THE FRACTIONATION ZONE WITH SULFURIC ACID, INTRODUCING THETREATED MATERIAL TO A SECOND FRACTIONATION ZONE WHEREIN HEAVIERCOMPONENTS ARE SEPARATED FROM THE CYCLOHEXANE AND RECOVERING FROM SAIDSECOND ZONE AND OVERHEAD PRODUCT CONTAINING NOT MORE THAN 11 VOLUMEPERCENT OF MATERIALS BOILING BELOW CYCLOHEXANE AND NOT MORE THAN ABOUT 6VOLUME PERCENT OF MATERIALS BOILING ABOVE CYCLOHEXANE.